Tower defense games started about thirty years ago during the arcade video games era. It typically requires a user to defend a territory or possession from enemy attacks. Alternatively, a user wins by destroying the opponent's territory or possession. Some tower defense games are real-time strategy games while others include aspects of turn-based strategy. Strategic selection and positioning of defensive elements is an important element of these games. Tower defense games saw increased popularity in the last decade due in part to the widespread use of smartphones and tablets.